Hi,
recently we switch on our Tarragon board (i.MX6ULL) to Linux 6.1 and
noticed that the connected 1-wire temperature sensors
(w1_therm.w1_strong_pull=0) sometimes (~ 1 of 20 times) report 85
degrees Celsius, which is AFAIK the only way to report errors to the
1-wire master:
sys/bus/w1/devices/28-04168158faff# cat w1_slave
50 05 4b 46 7f ff 0c 10 1c : crc=1c YES
50 05 4b 46 7f ff 0c 10 1c t=85000
I wasn't able to reproduce this issue with the old kernel 4.9.
After that i successfully bisected the issue to this commit:
67b392f7b8ed ("w1_therm: optimizing temperature read timings")
Unfortunately this commit contains a lot of independent changes, which
makes it hard to figured out the cause of this issue. So i tried to
split this patch in seven independent changes [1]. Now i was able to
bisect the cause further to this change [2] which seems to rework the
pullup handling within read_therm().
Looking closer at the code change and verify it some debug messages, the
change inverted the locking behavior (before: no pullup -> keep lock,
after: no pullup -> release lock during sleep).
Before:
if (external_power) {
mutex_unlock(&dev_master->bus_mutex);
sleep_rem = msleep_interruptible(tm);
if (sleep_rem != 0) {
ret = -EINTR;
goto dec_refcnt;
}
ret = mutex_lock_interruptible(&dev_master->bus_mutex);
if (ret != 0)
goto dec_refcnt;
} else if (!w1_strong_pullup) {
sleep_rem = msleep_interruptible(tm);
if (sleep_rem != 0) {
ret = -EINTR;
goto mt_unlock;
}
}
After:
if (strong_pullup) { /*some device need pullup */
sleep_rem = msleep_interruptible(tm);
if (sleep_rem != 0) {
ret = -EINTR;
goto mt_unlock;
}
} else { /*no device need pullup */
mutex_unlock(&dev_master->bus_mutex);
sleep_rem = msleep_interruptible(tm);
if (sleep_rem != 0) {
ret = -EINTR;
goto dec_refcnt;
}
ret = mutex_lock_interruptible(&dev_master->bus_mutex);
if (ret != 0)
goto dec_refcnt;
}
I don't believe this is intended. After inverting the strong_pullup
check, the issue wasn't reproducible on our platform anymore. But i'm
not sure this is clean.
Best regards
#regzbot introduced: 67b392f7b8ed
[1] - https://github.com/chargebyte/linux/commits/v6.1-tarragon_w1
[2] -
https://github.com/chargebyte/linux/commit/17ca863a32a6a1bdd376959f05c954bef12fc1b5
On Wed, Apr 26, 2023 at 03:39:15PM +0200, Stefan Wahren wrote:
> Hi,
>
> recently we switch on our Tarragon board (i.MX6ULL) to Linux 6.1 and noticed
> that the connected 1-wire temperature sensors (w1_therm.w1_strong_pull=0)
> sometimes (~ 1 of 20 times) report 85 degrees Celsius, which is AFAIK the
> only way to report errors to the 1-wire master:
>
> sys/bus/w1/devices/28-04168158faff# cat w1_slave
> 50 05 4b 46 7f ff 0c 10 1c : crc=1c YES
> 50 05 4b 46 7f ff 0c 10 1c t=85000
>
> I wasn't able to reproduce this issue with the old kernel 4.9.
>
> After that i successfully bisected the issue to this commit:
> 67b392f7b8ed ("w1_therm: optimizing temperature read timings")
>
> Unfortunately this commit contains a lot of independent changes, which makes
> it hard to figured out the cause of this issue. So i tried to split this
> patch in seven independent changes [1]. Now i was able to bisect the cause
> further to this change [2] which seems to rework the pullup handling within
> read_therm().
>
> Looking closer at the code change and verify it some debug messages, the
> change inverted the locking behavior (before: no pullup -> keep lock, after:
> no pullup -> release lock during sleep).
>
> Before:
> if (external_power) {
> mutex_unlock(&dev_master->bus_mutex);
>
> sleep_rem = msleep_interruptible(tm);
> if (sleep_rem != 0) {
> ret = -EINTR;
> goto dec_refcnt;
> }
>
> ret = mutex_lock_interruptible(&dev_master->bus_mutex);
> if (ret != 0)
> goto dec_refcnt;
> } else if (!w1_strong_pullup) {
> sleep_rem = msleep_interruptible(tm);
> if (sleep_rem != 0) {
> ret = -EINTR;
> goto mt_unlock;
> }
> }
>
> After:
> if (strong_pullup) { /*some device need pullup */
> sleep_rem = msleep_interruptible(tm);
> if (sleep_rem != 0) {
> ret = -EINTR;
> goto mt_unlock;
> }
> } else { /*no device need pullup */
> mutex_unlock(&dev_master->bus_mutex);
>
> sleep_rem = msleep_interruptible(tm);
> if (sleep_rem != 0) {
> ret = -EINTR;
> goto dec_refcnt;
> }
>
> ret = mutex_lock_interruptible(&dev_master->bus_mutex);
> if (ret != 0)
> goto dec_refcnt;
> }
>
> I don't believe this is intended. After inverting the strong_pullup check,
> the issue wasn't reproducible on our platform anymore. But i'm not sure this
> is clean.
>
> Best regards
>
> #regzbot introduced: 67b392f7b8ed
>
> [1] - https://github.com/chargebyte/linux/commits/v6.1-tarragon_w1
> [2] - https://github.com/chargebyte/linux/commit/17ca863a32a6a1bdd376959f05c954bef12fc1b5
Can you send a patch that shows the change you wish to have made here so
that you can get credit for fixing the issue?
thanks,
greg k-h
> Can you send a patch that shows the change you wish to have made here so
> that you can get credit for fixing the issue?
Sure, just for reference:
https://lore.kernel.org/lkml/[email protected]/T/
>
> thanks,
>
> greg k-h
On 26.04.23 15:39, Stefan Wahren wrote:
> recently we switch on our Tarragon board (i.MX6ULL) to Linux 6.1 and
> noticed that the connected 1-wire temperature sensors
> (w1_therm.w1_strong_pull=0) sometimes (~ 1 of 20 times) report 85
> degrees Celsius, which is AFAIK the only way to report errors to the
> 1-wire master:
> [...]
> #regzbot introduced: 67b392f7b8ed
#regzbot fix: w1_therm: optimizing temperature read timings
#regzbot ignore-activity
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
That page also explains what to do if mails like this annoy you.